Method and user equipment for transmitting uplink signals

ABSTRACT

In the present invention, a user equipment (UE) receives an UL grant that can be used while the UE is not in RRC_CONNECTED state. If the UE receives a message indicating to leave RRC_CONNECTED state, the UE starts a time alignment timer (I-TAT) when the UE leaves RRC_CONNECTED state. The UE transmits UL data using the UL grant if the UL data becomes available for transmission when the UE is not in RRC_CONNECTED state and if the I-TAT is running.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for transmitting uplink signals and anapparatus therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

As more and more communication devices demand larger communicationcapacity, there is a need for improved mobile broadband communicationcompared to existing RAT. Also, massive machine type communication(MTC), which provides various services by connecting many devices andobjects, is one of the major issues to be considered in the nextgeneration communication. In addition, a communication system designconsidering a service/UE sensitive to reliability and latency is beingdiscussed. The introduction of next-generation RAT, which takes intoaccount such advanced mobile broadband communication, massive MTC(mMCT), and ultra-reliable and low latency communication (URLLC), isbeing discussed.

DISCLOSURE Technical Problem

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

With development of technologies, overcoming delay or latency has becomean important challenge. Applications whose performance criticallydepends on delay/latency are increasing. Accordingly, a method to reducedelay/latency compared to the legacy system is demanded.

Also, with development of smart devices, a new scheme for efficientlytransmitting/receiving a small amount of data or efficientlytransmitting/receiving data occurring at a low frequency is required.

Also, a method for transmitting/receiving signals effectively in asystem supporting new radio access technology is required.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

In an aspect of the present invention, provided herein is a method oftransmitting, by a user equipment (UE), uplink (UL) signals in awireless communication system. The method comprises: receiving, by theUE, an UL grant that can be used while the UE is not in RRC_CONNECTEDstate; receiving, by the UE, a message indicating to leave RRC_CONNECTEDstate; starting, by the UE, a time alignment timer (I-TAT) when the UEleaves RRC_CONNECTED state; and transmitting, by the UE, UL data usingthe UL grant if the UL data becomes available for transmission when theUE is not in RRC_CONNECTED state and if the I-TAT is running.

In another aspect of the present invention, provided herein is a userequipment (UE) for transmitting uplink (UL) signals in a wirelesscommunication system. The UE comprises a radio frequency (RF) unit, anda processor configured to control the RF unit. The processor isconfigured to control the RF unit to receive an UL grant that can beused while the UE is not in RRC_CONNECTED state; control the RF unit toreceive a message indicating to leave RRC_CONNECTED state; start a timealignment timer (I-TAT) when the UE leaves RRC_CONNECTED state; andcontrol the RF unit to transmit UL data using the UL grant if the ULdata becomes available for transmission when the UE is not inRRC_CONNECTED state and if the I-TAT is running.

In each aspect of the present invention, if the UL data becomesavailable for transmission when the UE is not in RRC_CONNECTED state andif the I-TAT is not running, the UE may initiate a random access (RA)procedure.

In each aspect of the present invention, the UE may receive anindication to restart the I-TAT via system information. The UE mayrestart the I-TAT if receiving the indication.

In each aspect of the present invention, the I-TAT may be a durationwhere the UE considers that UL timing is synchronized while the UE isnot in RRC_CONNECTED state.

In each aspect of the present invention, the UE's leaving RRC_CONNECTEDstate may be the UE's entering RRC_INACTIVE state.

In each aspect of the present invention, the UL data may be transmittedwith an identity of the UE using the UL grant when the UE is not inRRC_CONNECTED state.

In each aspect of the present invention, the UE may stop the I-TAT whenthe UE enters RRC_CONNECTED state.

The above technical solutions are merely some parts of the embodimentsof the present invention and various embodiments into which thetechnical features of the present invention are incorporated can bederived and understood by persons skilled in the art from the followingdetailed description of the present invention.

Advantageous Effects

According to the present invention, radio communication signals can beefficiently transmitted/received. Therefore, overall throughput of aradio communication system can be improved.

According to one embodiment of the present invention, a lowcost/complexity UE can perform communication with a base station (BS) atlow cost while maintaining compatibility with a legacy system.

According to one embodiment of the present invention, the UE can beimplemented at low cost/complexity.

According to one embodiment of the present invention, the UE and the BScan perform communication with each other at a narrowband.

According to an embodiment of the present invention, delay/latencyoccurring during communication between a user equipment and a BS may bereduced.

Also, it is possible to efficiently transmit/receive a small amount ofdata for smart devices, or efficiently transmit/receive data occurringat a low frequency.

Also, signals in a new radio access technology system can betransmitted/received effectively.

According to an embodiment of the present invention, a small amount ofdata may be efficiently transmitted/received.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system.

FIG. 2 is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS).

FIG. 3 is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

FIG. 4 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard.

FIG. 5 is a view showing an example of a physical channel structure usedin an E-UMTS system.

FIG. 6 is a flow diagram showing an example of UL data transmissionaccording to the present invention.

FIG. 7 is a block diagram illustrating elements of a transmitting device100 and a receiving device 200 for implementing the present invention.

MODE FOR INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

In the present invention, the term “assume” may mean that a subject totransmit a channel transmits the channel in accordance with thecorresponding “assumption.” This may also mean that a subject to receivethe channel receives or decodes the channel in a form conforming to the“assumption,” on the assumption that the channel has been transmittedaccording to the “assumption.”

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port or avirtual antenna.

In the present invention, a cell refers to a prescribed geographicalarea to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell.

Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a cell in orderto manage radio resources and a cell associated with the radio resourcesis distinguished from a cell of a geographic region.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide service using a carrier and a “cell” of a radioresource is associated with bandwidth (BW) which is a frequency rangeconfigured by the carrier. Since DL coverage, which is a range withinwhich the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, the coverage of the node may be associated with coverage of the“cell” of a radio resource used by the node. Accordingly, the term“cell” may be used to indicate service coverage of the node sometimes, aradio resource at other times, or a range that a signal using a radioresource can reach with valid strength at other times.

Meanwhile, the 3GPP LTE-A standard uses the concept of a cell to manageradio resources. The “cell” associated with the radio resources isdefined by combination of downlink resources and uplink resources, thatis, combination of DL component carrier (CC) and UL CC. The cell may beconfigured by downlink resources only, or may be configured by downlinkresources and uplink resources. If carrier aggregation is supported,linkage between a carrier frequency of the downlink resources (or DL CC)and a carrier frequency of the uplink resources (or UL CC) may beindicated by system information. For example, combination of the DLresources and the UL resources may be indicated by linkage of systeminformation block type 2 (SIB2). In this case, the carrier frequencymeans a center frequency of each cell or CC. A cell operating on aprimary frequency may be referred to as a primary cell (Pcell) or PCC,and a cell operating on a secondary frequency may be referred to as asecondary cell (Scell) or SCC. The carrier corresponding to the Pcell ondownlink will be referred to as a downlink primary CC (DL PCC), and thecarrier corresponding to the Pcell on uplink will be referred to as anuplink primary CC (UL PCC). A Scell means a cell that may be configuredafter completion of radio resource control (RRC) connectionestablishment and used to provide additional radio resources. The Scellmay form a set of serving cells for the UE together with the Pcell inaccordance with capabilities of the UE. The carrier corresponding to theScell on the downlink will be referred to as downlink secondary CC (DLSCC), and the carrier corresponding to the Scell on the uplink will bereferred to as uplink secondary CC (UL SCC). Although the UE is inRRC-CONNECTED state, if it is not configured by carrier aggregation ordoes not support carrier aggregation, a single serving cell configuredby the Pcell only exists.

In the present invention, “PDCCH” refers to a PDCCH, a EPDCCH (insubframes when configured), a MTC PDCCH (MPDCCH), for an RN with R-PDCCHconfigured and not suspended, to the R-PDCCH or, for NB-IoT to thenarrowband PDCCH (NPDCCH).

In the present invention, for dual connectivity operation the term“special Cell” refers to the PCell of the master cell group (MCG) or thePSCell of the secondary cell group (SCG), otherwise the term SpecialCell refers to the PCell. The MCG is a group of serving cells associatedwith a master eNB (MeNB) which terminates at least S1-MME, and the SCGis a group of serving cells associated with a secondary eNB (SeNB) thatis providing additional radio resources for the UE but is not the MeNB.The SCG is comprised of a primary SCell (PSCell) and optionally one ormore SCells. In dual connectivity, two MAC entities are configured inthe UE: one for the MCG and one for the SCG. Each MAC entity isconfigured by RRC with a serving cell supporting PUCCH transmission andcontention based Random Access. In this specification, the term SpCellrefers to such cell, whereas the term SCell refers to other servingcells. The term SpCell either refers to the PCell of the MCG or thePSCell of the SCG depending on if the MAC entity is associated to theMCG or the SCG, respectively.

In the present invention, “C-RNTI” refers to a cell RNTI, “G-RNTI”refers to a group RNTI, “P-RNTI” refers to a paging RNTI, “RA-RNTI”refers to a random access RNTI, “SC-RNTI” refers to a single cell RNTI”,“SL-RNTI” refers to a sidelink RNTI, and “SPS C-RNTI” refers to asemi-persistent scheduling C-RNTI.

For terms and technologies which are not specifically described amongthe terms of and technologies employed in this specification, 3GPPLTE/LTE-A standard documents, for example, 3GPP TS 36.211, 3GPP TS36.212, 3GPP TS 36.213, 3GPP TS 36.300, 3GPP TS 36.321, 3GPP TS 36.322,3GPP TS 36.323 and 3GPP TS 36.331 may be referenced.

FIG. 2 is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNB 20 to UE 10,and “uplink” refers to communication from the UE to an eNB.

FIG. 3 is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 3, an eNB 20 provides end points of a user planeand a control plane to the UE 10. MME/SAE gateway 30 provides an endpoint of a session and mobility management function for UE 10. The eNBand MME/SAE gateway may be connected via an Si interface.

The eNB 20 is generally a fixed station that communicates with a UE 10,and may also be referred to as a base station (BS) or an access point.One eNB 20 may be deployed per cell. An interface for transmitting usertraffic or control traffic may be used between eNBs 20.

The MME provides various functions including NAS signaling to eNBs 20,NAS signaling security, AS Security control, Inter CN node signaling formobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, roaming,authentication, bearer management functions including dedicated bearerestablishment, support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNB 20 and gateway 30 viathe S1 interface. The eNBs 20 may be connected to each other via an X2interface and neighboring eNBs may have a meshed network structure thathas the X2 interface.

As illustrated, eNB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 4 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

Layer 1 (i.e. L1) of the LTE/LTE-A system is corresponding to a physicallayer. A physical (PHY) layer of a first layer (Layer 1 or L1) providesan information transfer service to a higher layer using a physicalchannel The PHY layer is connected to a medium access control (MAC)layer located on the higher layer via a transport channel Data istransported between the MAC layer and the PHY layer via the transportchannel. Data is transported between a physical layer of a transmittingside and a physical layer of a receiving side via physical channels. Thephysical channels use time and frequency as radio resources. In detail,the physical channel is modulated using an orthogonal frequency divisionmultiple access (OFDMA) scheme in downlink and is modulated using asingle carrier frequency division multiple access (SC-FDMA) scheme inuplink.

Layer 2 (i.e. L2) of the LTE/LTE-A system is split into the followingsublayers: Medium Access Control (MAC), Radio Link Control (RLC) andPacket Data Convergence Protocol (PDCP). The MAC layer of a second layer(Layer 2 or L2) provides a service to a radio link control (RLC) layerof a higher layer via a logical channel. The RLC layer of the secondlayer supports reliable data transmission. A function of the RLC layermay be implemented by a functional block of the MAC layer. A packet dataconvergence protocol (PDCP) layer of the second layer performs a headercompression function to reduce unnecessary control information forefficient transmission of an Internet protocol (IP) packet such as an IPversion 4 (IPv4) packet or an IP version 6 (IPv6) packet in a radiointerface having a relatively small bandwidth.

Layer 3 (i.e. L3) of the LTE/LTE-A system includes the followingsublayers: Radio Resource Control (RRC) and Non Access Stratum (NAS). Aradio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other. The non-access stratum (NAS) layer positioned over the RRClayer performs functions such as session management and mobilitymanagement.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 5 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 5, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

A time interval in which one subframe is transmitted is defined as atransmission time interval (TTI). Time resources may be distinguished bya radio frame number (or radio frame index), a subframe number (orsubframe index), a slot number (or slot index), and the like. TTI refersto an interval during which data may be scheduled. For example, in thecurrent LTE/LTE-A system, a opportunity of transmission of an UL grantor a DL grant is present every 1 ms, and the UL/DL grant opportunitydoes not exists several times in less than 1 ms. Therefore, the TTI inthe current LTE/LTE-A system is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

If a UE is powered on or newly enters a cell, the UE performs an initialcell search procedure of acquiring time and frequency synchronizationwith the cell and detecting a physical cell identity N^(cell) _(ID) ofthe cell. To this end, the UE may establish synchronization with the eNBby receiving synchronization signals, e.g. a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS), from the eNBand obtain information such as a cell identity (ID). The UE havingfinished initial cell search may perform the random access procedure tocomplete access to the eNB. To this end, the UE may transmit a preamblethrough a physical random access channel (PRACH), and receive a responsemessage which is a response to the preamble through a PDCCH and PDSCH.In the case of contention-based random access, transmission of anadditional PRACH and a contention resolution procedure for the PDCCH anda PDSCH corresponding to the PDCCH may be performed. After performingthe procedure described above, the UE may perform PDCCH/PDSCH receptionand PUSCH/PUCCH transmission as a typical procedure of transmission ofan uplink/downlink signal.

The random access procedure is also referred to as a random accesschannel (RACH) procedure. The random access procedure is commonprocedure for FDD and TDD, and one procedure irrespective of cell sizeand the number of serving cells when carrier aggregation (CA) isconfigured. The random access procedure is used for various purposesincluding initial access, adjustment of uplink synchronization, resourceassignment, and handover. Random access procedures are classified into acontention-based procedure and a dedicated (i.e., non-contention-based)procedure. The contention-based random access procedure is used forgeneral operations including initial access, while the dedicated randomaccess procedure is used for limited operations such as handover. In thecontention-based random access procedure, the UE randomly selects a RACHpreamble sequence. Accordingly, it is possible that multiple UEstransmit the same RACH preamble sequence at the same time. Thereby, acontention resolution procedure needs to be subsequently performed. Onthe other hand, in the dedicated random access procedure, the UE uses anRACH preamble sequence that the eNB uniquely allocates to the UE.Accordingly, the random access procedure may be performed withoutcontention with other UEs.

Hereinafter, description will be given of the RRC state of the UE. If anRRC connection is established between the RRC layer of the UE and theRRC layer of a wireless network, the UE is in the RRC_CONNECTED state.Otherwise, the UE is in the RRC_IDLE state. The RRC state refers to astate in which the RRC of the UE is or is not logically connected withthe RRC of the E-UTRAN. The RRC state of the UE having a logicalconnection with the RRC of the E-UTRAN is referred to as anRRC_CONNECTED state. The RRC state of the UE which does not have alogical connection with the RRC of the E-UTRAN is referred to as anRRC_IDLE state. A UE in RRC_CONNECTED has a RRC connection, and thus theE-UTRAN may recognize presence of the UE in a cell unit. Accordingly,the UE may be efficiently controlled. On the other hand, the E-UTRANcannot recognize presence of a UE which is in RRC_IDLE. The UE inRRC_IDLE is managed by a core network in a tracking area (TA) which isan area unit larger than the cell. That is, for the UE in RRC_IDLE, onlypresence or absence of the UE is recognized in an area unit larger thanthe cell. In order for the UE in RRC_IDLE to be provided with a usualmobile communication service such as a voice service and a data service,the UE should transition to the RRC_CONNECTED state. A TA isdistinguished from another TA by a tracking area identity (TAI) thereof.A UE may configure the TAI through a tracking area code, which isinformation broadcast from a cell. When the user initially turns on theUE, the UE searches for a proper cell first. Then, the UE establishes anRRC connection in the cell and registers information thereabout in thecore network. Thereafter, the UE stays in the RRC_IDLE state. Whennecessary, the UE staying in the RRC_IDLE state selects a cell (again)and checks system information or paging information. This operation iscalled camping on a cell. Only when the UE staying in the RRC_IDLE stateneeds to establish an RRC connection, does the UE establish an RRCconnection with the RRC layer of the E-UTRAN through the RRC connectionprocedure and transition to the RRC_CONNECTED state. The UE staying inthe RRC_IDLE state needs to establish RRC connection in many cases. Forexample, the cases may include an attempt of a user to make a phonecall, an attempt to transmit data, or transmission of a response messageafter reception of a paging message from the E-UTRAN.

The RRC layer uses the RRC_IDLE state for PLMN selection, DRX configuredby NAS, broadcast of system information, paging, cell re-selection. Fora UE in RRC_IDLE, a UE specific DRX may be configured by NAS (notapplicable for NB-IoT). The UE in RRC_IDLE can perform UE controlledmobility. The UE in RRC_IDLE monitors a paging channel to detectincoming calls, system information change, for earthquake and tsunamiwarning system (ETWS) capable UEs, ETWS notification, and for commercialmobility alert service (CMAS) capable UEs, CMAS notification, performsneighboring cell measurements and cell (re-)selection, acquires systeminformation, performs logging of available measurements together withlocation and time for logged measurement configured UEs. No RRC contextstored in the eNB (except for a UE that supports user plane CIoT EPSoptimizations where a context may be stored for the resume procedure),sidelink communication transmission and reception, and/or sidelinkdiscovery announcement and monitoring.

A UE in RRC_CONNECTED has an E-UTRAN-RRC connection and context inE-UTRAN. A UE in RRC_CONNECTED can perform network controlled mobility(handover and inter-RAT cell change order to GERAN with NACC), neighborcell measurements. E-UTRAN knows the cell which the UE in RRC_CONNECTEDbelongs to, sidelink communication transmission and reception, andsidelink discovery announcement and monitoring. The network can transmitand/or receive data to/from the UE in RRC_CONNECTED. At PDCP/RLC/MAClevel, the UE in RRC_CONNECTED can transmit and/or receive data to/fromthe network; monitors control signaling channel for shared data channelto see if any transmission over the shared data channel has beenallocated to the UE; reports channel quality information and feedbackinformation to the eNB. In RRC_CONNECTED, a DRX period can be configuredaccording to the UE activity level for the UE power saving and efficientresource utilization under control of the eNB. The UE in RRC_CONNECTEDmonitors a paging channel and/or system information block type 1contents to detect system information change, for ETWS capable UEs, ETWSnotification, and for CMAS capable UEs, CMAS notification (notapplicable for NB-IoT); monitors control channels associated with theshared data channel to determine if data is scheduled to it; provideschannel quality and feedback information (not applicable for NB-IoT);performs neighboring cell measurements and measurements reporting (notapplicable for NB-IoT); and acquires system information. Referring to3GPP TS 36.331, upon leaving RRC_CONNECTED, the UE shall:

-   -   1> reset MAC;    -   1> stop all timers that are running except T320, T325 and T330;    -   1> if leaving RRC_CONNECTED was triggered by suspension of the        RRC:        -   2> re-establish RLC entities for all SRBs and DRBs;        -   2> store the UE AS Context including the current RRC            configuration, the current security context, the PDCP state            including ROHC state, C-RNTI used in the source PCell, the            cellIdentity and the physical cell identity of the source            PCell;        -   2> store the following information provided by E-UTRAN:            -   3> the resumeIdentity;        -   2> suspend all SRB(s) and DRB(s);        -   2> indicate the suspension of the RRC connection to upper            layers;    -   1> else:        -   2> release all radio resources, including release of the RLC            entity, the MAC configuration and the associated PDCP entity            for all established RBs;        -   2> indicate the release of the RRC connection to upper            layers together with the release cause;    -   1> if leaving RRC_CONNECTED was triggered neither by reception        of the MobilityFromEUTRACommand message nor by selecting an        inter-RAT cell while T311 was running:        -   2> if timer T350 is configured:            -   3> start timer T350;            -   3> apply rclwi-Configuration if configured, otherwise                apply the wlan-Id-List corresponding to the RPLMN                included in SystemInformationBlockType17;        -   2> else:            -   3> release the wlan-OffloadConfigDedicated, if received;            -   3> if the wlan-OffloadConfigCommon corresponding to the                RPLMN is broadcast by the cell:                -   4> apply the wlan-OffloadConfigCommon corresponding                    to the RPLMN included in                    SystemInformationBlockType17;                -   4> apply steerToWLAN if configured, otherwise apply                    the wlan-Id-List corresponding to the RPLMN included                    in SystemInformationBlockType17;        -   2> enter RRC_IDLE and perform procedures as specified in            3GPP TS 36.304;    -   1> else:        -   2> release the wlan-OffloadConfigDedicated, if received;    -   1> indicate the release of LWA configuration, if configured, to        upper layers;    -   1> release the LWIP configuration, if configured.

Referring to 3GPP TS 36.321, if a reset of the MAC entity is requestedby upper layers (e.g. RRC layer), the MAC entity initializes Bj for eachlogical channel to zero; stops (if running) all timers; considers alltimeAlignmentTimers as expired and perform the corresponding actions;sets the new data indicators (NDIs) for all uplink HARQ processes to thevalue 0; stops, if any, ongoing RACH procedure; discards explicitlysignalled ra-PreambleIndex and ra-PRACH-MaskIndex, if any; flushes Msg3buffer; cancels, if any, triggered Scheduling Request procedure;cancels, if any, triggered Buffer Status Reporting procedure; cancels,if any, triggered Power Headroom Reporting procedure; flushes the softbuffers for all DL HARQ processes; for each DL HARQ process, considersthe next received transmission for a transport block (TB) as the veryfirst transmission; releases, if any, Temporary C-RNTI.

In the legacy LTE system, the value for timeAlignmentTimer is providedvia system information block type 2 (SIB2) containing radio resourceconfiguration information that is common for all UEs, or via a RRCdedicated signaling. The value for timeAlignmentTimer is provided innumber of subframes.

In RRC_CONNECTED, the eNB is responsible for maintaining the timingadvance. Serving cells having UL to which the same timing advanceapplies (typically corresponding to the serving cells hosted by the samereceiver) and using the same timing reference cell are grouped in atiming advance group (TAG). In other words, a TAG is a group of servingcells that is configured by RRC and that, for the cells with an ULconfigured, use the same timing reference cell and the same TA value.Each TAG contains at least one serving cell with configured uplink, andthe mapping of each serving cell to a TAG is configured by RRC. In caseof dual connectivity (DC), a TAG only includes cells that are associatedto the same CG and the maximum number of TAG is 8. For the primary TAG(pTAG) the UE uses the PCell in a master cell group (MCG) and the PSCellin a secondary cell group (SCG) as timing reference. In a secondary TAG(sTAG), the UE may use any of the activated SCells of this TAG as atiming reference cell, but should not change it unless necessary. Insome cases (e.g. during DRX), the timing advance is not necessarilyalways maintained and the MAC sublayer knows if the L1 is synchronisedand which procedure to use to start transmitting in the uplink. As longas the L1 is non-synchronised, uplink transmission can only take placeon PRACH. For a TAG, cases where the UL synchronisation status movesfrom “synchronised” to “non-synchronised” include expiration of a timerspecific to the TAG, and non-synchronised handover. The MAC entity has aconfigurable timer timeAlignmentTimer per timing advance group (TAG).The timeAlignmentTimer is used to control how long the MAC entityconsiders the serving cells belonging to the associated TAG to be uplinktime aligned. The value of the timer associated to the pTAG of MCG iseither UE specific and managed through dedicated signalling between theUE and the eNB, or cell specific and indicated via broadcastinformation. In both cases, the timer is normally restarted whenever anew timing advance is given by the eNB for the pTAG. The value of thetimer associated to a pTAG of SCG and the value of a timer associated toan sTAG of an MCG or an sTAG of SCG are managed through dedicatedsignalling between the UE and the eNB, and the timers associated tothese TAGs can be configured with different values. The timers of theseTAGs are normally restarted whenever a new timing advance is given bythe eNB for the corresponding TAG.

When a timing advance command MAC control element is received, the MACentity applies the timing advance command for the indicated TAG; andstarts or restarts the timeAlignmentTimer associated with the indicatedTAG. In other words, when a timing advance MAC control element isreceived, the MAC entity adjusts the subframe boundary according to thetiming advance command for the indicated TAG, and starts or restarts thetimeAlignmentTimer associated with the indicated TAG. The timing advancecommand (TAC) MAC control element (CE) contains a TAG identity and atiming advance command. The TAG identity indicates the TAG identity ofthe addressed TAG. The timing advance command in the TAC MAC CEindicates the index value T_(A) used to control the amount of timingadjustment that the MAC entity has to apply.

Upon reception of a timing advance command for a TAG containing theprimary cell or PSCell, the UE adjusts uplink transmission timing forPUCCH/PUSCH/SRS of the primary cell or PSCell based on the receivedtiming advance command The timing advance command for a TAG indicatesthe change of the uplink timing relative to the current uplink timingfor the TAG as multiples of 16 T_(s), where T_(s) is a basic time unit.In the legacy LTE system, T_(s)=1/(15000*2048) seconds, normally. Incase of random access response, an 11-bit timing advance command, T_(A),for a TAG indicates N_(TA) values by index values of T_(A)=0, 1, 2, . .. , 256 if the UE is configured with a SCG, and T_(A)=0, 1, 2, . . . ,1282 otherwise, where an amount of the time alignment for the TAG isgiven by N_(TA)=T_(A)*16. N_(TA) is a timing offset between uplink anddownlink radio frames at the UE, expressed in units of T. In othercases, a 6-bit timing advance command, T_(A), for a TAG indicatesadjustment of the current N_(TA) value, N_(TA,old), to the new N_(TA)value, N_(TA,new), by index values of T_(A)=0, 1, 2, . . . , 63, whereN_(TA,new)=N_(TA,old)+(T_(A)−31)*16. Here, adjustment of T_(A) value bya positive or a negative amount indicates advancing or delaying theuplink transmission timing for the TAG by a given amount respectively.For a timing advance command received on subframe n, the correspondingadjustment of the uplink transmission timing applies from the beginningof subframe n+6. Transmission of the uplink radio frame i from the UEshall start (N_(TA)+N_(TAoffset))*T_(s) seconds before the start of thecorresponding downlink radio frame at the UE, where 0≤N_(TA)≤4096 if theUE is configured with a secondary cell group (SCG) and 0≤N_(TA)≤20512otherwise. N_(TAoffset) is a fixed timing advance offset, expressed inunits of T_(s) (see 3GPP TS 36.211).

When a timeAlignmentTimer expires, if the timeAlignmentTimer isassociated with the pTAG, the MAC entity flushes all HARQ buffers forall serving cells; notifies RRC to release PUCCH for all serving cells;notifies RRC to release SRS for all serving cells; clears any configureddownlink assignments and uplink grants; considers all runningtimeAlignmentTimers as expired. When a timeAlignmentTimer expires, ifthe timeAlignmentTimer is associated with an sTAG, then for all servingcells belonging to this TAG, the MAC entity flushes all HARQ buffers;notifies RRC to release SRS; and notifies RRC to release PUCCH, ifconfigured.

When the MAC entity stops uplink transmissions for an SCell due to thefact that the maximum uplink transmission timing difference (asdescribed in subclause 7.9.2 of 3GPP TS 36.133) or the maximum uplinktransmission timing difference the UE can handle between TAGs of any MACentity of the UE is exceeded, the MAC entity considers thetimeAlignmentTimer associated with the SCell as expired. The MAC entityshall not perform any uplink transmission on a Serving Cell except theRandom Access Preamble transmission when the timeAlignmentTimerassociated with the TAG to which this serving cell belongs is notrunning Furthermore, when the timeAlignmentTimer associated with thepTAG is not running, the MAC entity shall not perform any uplinktransmission on any serving cell except the random access preambletransmission on the SpCell. The MAC entity shall not perform anysidelink transmission which is performed based on UL timing of thecorresponding serving cell and any associated SCI transmissions when thecorresponding timeAlignmentTimer is not running A MAC entity stores ormaintains N_(TA) upon expiry of associated timeAlignmentTimer, whereN_(TA) is defined in 3GPP TS 36.211. The MAC entity applies a receivedtiming advance command MAC control element and starts associatedtimeAlignmentTimer also when the timeAlignmentTimer is not running.

In order to transmit on the UL-SCH the MAC entity must have a validuplink grant (except for non-adaptive HARQ retransmissions) which it mayreceive dynamically on the PDCCH or in a Random Access Response or whichmay be configured semi-persistently. To perform requested transmissions,the MAC layer receives HARQ information from lower layers. When thephysical layer is configured for uplink spatial multiplexing, the MAClayer can receive up to two grants (one per HARQ process) for the sameTTI from lower layers.

A fully mobile and connected society is expected in the near future,which will be characterized by a tremendous amount of growth inconnectivity, traffic volume and a much broader range of usagescenarios. Some typical trends include explosive growth of data traffic,great increase of connected devices and continuous emergence of newservices. Besides the market requirements, the mobile communicationsociety itself also requires a sustainable development of theeco-system, which produces the needs to further improve systemefficiencies, such as spectrum efficiency, energy efficiency,operational efficiency and cost efficiency. To meet the aboveever-increasing requirements from market and mobile communicationsociety, next generation access technologies are expected to emerge inthe near future.

Work has started in ITU and 3GPP to develop requirements andspecifications for new radio systems, as in the Recommendation ITU-RM.2083 “Framework and overall objectives of the future development ofIMT for 2020 and beyond”, as well as 3GPP SA1 study item New Servicesand Markets Technology Enablers (SMARTER) and SA2 study itemArchitecture for the new RAT (NR) System (also referred to as 5G newRAT). It is required to identify and develop the technology componentsneeded for successfully standardizing the NR system timely satisfyingboth the urgent market needs, and the more long-term requirements setforth by the ITU-R IMT-2020 process. In order to achieve this,evolutions of the radio interface as well as radio network architecturehave to be considered in the “New Radio Access Technology.”

In 5G New RAT, a new state, called RRC_INACTIVE, is introduced inaddition to RRC_IDLE and RRC_CONNECTED. The benefit of keeping UE inRRC_INACTIVE is as follows:

-   -   as the UE context is stored in the radio access network (RAN),        the core network (CN) signaling could be reduced when RRC        connection is established;    -   as the UE is tracked in RAN level, the paging overhead could be        reduced;    -   as the UE is configured with DRX similar to RRC_IDLE, the UE        power consumption could be reduced.

To fully enjoy the benefit of the RRC_INACTIVE, however, it is requiredthat the UE should be able to transmit small data in the RRC_INACTIVEstate without state transition to the RRC_CONNECTED state. The statetransition to RRC_CONNECTED requires couple of handshakes of RRCmessages, which consumes much radio resource and UE power. Moreover, ifthe UE is kept in RRC_CONNECTED, the UE consumes more power thanRRC_INACTIVE because the connected mode DRX is less power efficient thanidle (or inactive) mode DRX. Accordingly, in this RRC_INACTIVE state,the UE may need to transmit UL data using contention based UL grant(hereinafter, CB-grant). For the UE to perform UL transmission, the UEmust have valid uplink timing. If the UL transmission timing isde-synchronized between UE and eNB, this UE's UL transmitted data wouldact as interference to other UEs, and this UE's UL data as well as otherUE's data would not be correctly received by the eNB. The ULtransmission timing is controlled by a timer, called TimeAlignmentTimer(TAT). While the TAT is running, the UE considers that the UL timing issynchronized, and can perform UL transmission. However, if the TAT isnot running, the UE considers that the UL timing is not synchronized,and the UE has to perform an random access (RA) procedure beforeperforming UL transmission. During the RA procedure, the UE can acquireUL timing by a timing advance command (TAC) included in a random accessresponse message. In the current LTE, when the UE leaves RRC_CONNECTED,the UE resets MAC. If the MAC is reset, the TAT expires at the UE.Therefore, there is no running TAT if the UE is not in RRC_CONNECTED,and the UE cannot perform UL transmission. In order to solving theseproblems, the following method is proposed.

For the UE to perform UL transmission in other state than RRC_CONNECTED(i.e. RRC_INACTIVE or RRC_IDLE), the present invention proposes that theUE maintain another TimeAlignmentTimer (hereinafter, I-TAT), which isused in other state than RRC_CONNECTED, and perform UL transmission inother state than RRC_CONNECTED if the I-TAT is running In other words,while the I-TAT is running, the UE in other state than RRC_CONNECTEDconsiders that the UL timing is synchronized, and can perform ULtransmission. If the I-TAT is not running, the UE in other state thanRRC_CONNECTED does not perform UL transmission but performs a randomaccess procedure to acquire UL transmission timing before performing ULtransmission.

In the present invention, a UE may maintain an I-TAT for RRC_INACTIVEonly, an I-TAT for RRC_IDLE only, an I-TAT for RRC_INACTIVE and RRC_IDLEboth, or one for RRC_IDLE and one for RRC IDLE.

The UE may receive the value of I-TAT from the eNB via systeminformation, dedicated RRC signaling, or MAC control element. The UE mayreceive the value of I-TAT from the eNB when the UE leavesRRC_CONNECTED, when the UE enters RRC_CONNECTED, when the UE is inRRC_CONNECTED, when the UE enters RRC_INACTIVE, or when the UE entersRRC_IDLE.

In the legacy LTE system, a UE stops or terminates timers used inRRC_CONNECTED when the UE leaves RRC_CONNECTED. On the contrary to thelegacy LTE system, in the present invention, a UE starts the I-TAT whenthe UE leaves RRC_CONNECTED, when the UE enters RRC_INACTIVE, when theUE enters RRC_IDLE, when the UE resets MAC, or when the UE receives anindication to start I-TAT from the eNB via system information orRRC/PDCP/RLC/MAC signaling. The indication may be a timing advancecommand.

The UE restarts the I-TAT when the UE receives an indication to restartI-TAT from the eNB via system information or RRC/PDCP/RLC/MAC signaling.The indication may be a timing advance command.

The UE stops the I-TAT or the I-TAT expires, when the UE entersRRC_CONNECTED, when the UE leaves RRC_INACTIVE, or when the UE leavesRRC_IDLE.

When the I-TAT expires, the UE may consider that UL timing isde-synchronized, may not perform UL transmission, may release configuredUL grant that can be used for UL transmission in RRC_INACTIVE orRRC_IDLE, and/or flush all HARQ buffers for all serving cells.

FIG. 6 is a flow diagram showing an example of UL data transmissionaccording to the present invention.

When an UL data arrives (S620) at the UE in RRC_INACTIVE or RRC_IDLE(S610), the UE checks whether the I-TAT is running (S630). In otherwords, if the UL data becomes available for transmission when the UE isnot in RRC_CONNECTED, the UE checks whether the I-TAT is running.

If the I-TAT is running (S630, Yes), the UE performs UL transmissionusing the configured UL grant that can be used for UL transmission inRRC_INACTIVE or RRC_IDLE (S640). The configured UL grant is eithercontention based or dedicated. The UE may transmit the UE identity (ID)together with the UL data.

If the I-TAT is not running (S630, No), the UE considers that ULtransmission is not allowed, and initiates an RA procedure (S650).During the RA procedure, the UE receives a timing advance command (TAC)in a random access response message. If the RA procedure is successfullycompleted, the UE applies the TAC received in the RAR to the I-TAT andstarts the I-TAT. Then, as the I-TAT is running, the UE performs ULtransmission using the configured UL grant that can be used for ULtransmission in RRC_INACTIVE or RRC_IDLE.

The TAT used in RRC_CONNECTED may be reused as the I-TAT of the presentinvention.

The I-TAT of the present invention and the TAT used in RRC_CONNECTED maybe configured separately. A UE in RRC_INACTIVE can be tracked in RANlevel, and this means that UE does not move much. Considering this, thevalue for I-TAT may be configured larger than the value for the TAT usedin RRC_CONNECTED.

In the present invention, a UE in RRC_IDLE or RRC_INACTIVE can performUL transmission without the RA procedure if the I-TAT is runningAccordingly, radio resources are more effectively managed in RRC_IDLE orRRC_INACTIVE, and more effective UE power saving is achieved.

The present invention is different from the control plane CIoT EPSoptimization in that a UE of the present invention can perform ULtransmission in RRC_IDLE or RRC_INACTIVE without the RA procedure if theI-TAT is running, whereas a UE using the control plane CIoT EPSoptimization has to perform at least part of the RA procedure to performUL transmission since UL user data can be transmitted first through aNAS PDU in a RRC connection setup complete message according to thecontrol plane CIoT EPS optimization.

FIG. 7 is a block diagram illustrating elements of a transmitting device100 and a receiving device 200 for implementing the present invention.

The transmitting device 100 and the receiving device 200 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedembodiments of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 100 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into K layers through demultiplexing, channel coding,scrambling, and modulation. The coded data stream is also referred to asa codeword and is equivalent to a transport block which is a data blockprovided by a MAC layer. One transport block (TB) is coded into onecodeword and each codeword is transmitted to the receiving device in theform of one or more layers. For frequency up-conversion, the RF unit 13may include an oscillator. The RF unit 13 may include N_(t) (where N_(t)is a positive integer) transmit antennas.

A signal processing process of the receiving device 200 is the reverseof the signal processing process of the transmitting device 100. Undercontrol of the processor 21, the RF unit 23 of the receiving device 200receives radio signals transmitted by the transmitting device 100. TheRF unit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 100 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 200. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 200 and enables the receiving device 200 toderive channel estimation for the antenna, irrespective of whether thechannel represents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the embodiments of the present invention, a UE operates as thetransmitting device 100 in UL and as the receiving device 200 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 200 in UL and as the transmitting device 100 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

The UE processor according to present invention may control the UE RFunit to receive an UL grant that can be used while the UE is not inRRC_CONNECTED state. The UE processor may control the UE RF unit toreceive a message indicating to leave RRC_CONNECTED state. If the UE RFunit receives a message indicating to leave RRC_CONNECTED state, the UEprocessor may start a time alignment timer (I-TAT) when the UE leavesRRC_CONNECTED state. The UE processor may control the UL RF unit totransmit UL data using the UL grant if the UL data becomes available fortransmission when the UE is not in RRC_CONNECTED state and if the I-TATis running If the UL data becomes available for transmission when the UEis not in RRC_CONNECTED state and if the I-TAT is not running, the UEprocessor may initiate an RA procedure to get UL synchronization. The UEprocessor may control the UE RF unit to receive an indication to restartthe I-TAT via system information. If the UE RF unit receives theindication to restart the I-TAT, the UE may restart the I-TAT. the I-TATmay indicates a duration where the UE considers that UL timing issynchronized while the UE is not in RRC_CONNECTED state. UE's leavingRRC_CONNECTED state may mean UE's entering RRC_INACTIVE state. The UEprocessor may control the RF unit to transmit the UL data with anidentity of the UE using the UL grant when the UE is not inRRC_CONNECTED state. The UE processor may stop the I-TAT when the UEenters RRC_CONNECTED state. The message may include a value for the timealignment timer (I-TAT).

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to a networknode (e.g., BS), a UE, or other devices in a wireless communicationsystem.

1. A method for transmitting, by a user equipment (UE), uplink (UL)signals in a wireless communication system, the method comprising:receiving, by the UE, an UL grant that can be used while the UE is notin RRC_CONNECTED state; receiving, by the UE, a message indicating toleave RRC_CONNECTED state; starting, by the UE, a time alignment timer(I-TAT) when the UE leaves RRC_CONNECTED state; and transmitting, by theUE, UL data using the UL grant if the UL data becomes available fortransmission when the UE is not in RRC_CONNECTED state and if the I-TATis running
 2. The method according to claim 1, wherein if the UL databecomes available for transmission when the UE is not in RRC_CONNECTEDstate and if the I-TAT is not running, the UE initiates a random access(RA) procedure.
 3. The method according to claim 1, further comprising:receiving, by the UE, an indication to restart the I-TAT via systeminformation; and restarting, by the UE, the I-TAT.
 4. The methodaccording to claim 1, wherein the I-TAT is a duration where the UEconsiders that UL timing is synchronized while the UE is not inRRC_CONNECTED state.
 5. The method according to claim 1, wherein the UEleaving RRC_CONNECTED state is the UE entering RRC_INACTIVE state. 6.The method according to claim 1, wherein the UL data is transmitted withan identity of the UE using the UL grant when the UE is not inRRC_CONNECTED state.
 7. The method according to claim 1, stopping, bythe UE, the I-TAT when the UE enters RRC_CONNECTED state.
 8. The methodaccording to claim 1, wherein the message includes a value for the timealignment timer (I-TAT).
 9. A user equipment (UE) for transmittinguplink (UL) signals in a wireless communication system, the UEcomprising: a radio frequency (RF) unit, and a processor configured tocontrol the RF unit, the processor configured to: control the RF unit toreceive an UL grant that can be used while the UE is not inRRC_CONNECTED state; control the RF unit to receive a message indicatingto leave RRC_CONNECTED state; start a time alignment timer (I-TAT) whenthe UE leaves RRC_CONNECTED state; and control the RF unit to transmitUL data using the UL grant if the UL data becomes available fortransmission when the UE is not in RRC_CONNECTED state and if the I-TATis running.
 10. The UE according to claim 9, wherein if the UL databecomes available for transmission when the UE is not in RRC_CONNECTEDstate and if the I-TAT is not running, the processor is configured toinitiate a random access (RA) procedure.
 11. The UE according to claim9, wherein the processor is configured to: control the RF unit toreceive an indication to restart the I-TAT via system information; andrestart the I-TAT.
 12. The UE according to claim 9, wherein the I-TAT isa duration where the UE considers that UL timing is synchronized whilethe UE is not in RRC_CONNECTED state.
 13. The UE according to claim 9,wherein the UE leaving RRC_CONNECTED state is the UE enteringRRC_INACTIVE state.
 14. The UE according to claim 9, wherein theprocessor is configured to control the RF unit to transmit the UL datawith an identity of the UE using the UL grant when the UE is not inRRC_CONNECTED state.
 15. The UE according to claim 9, wherein theprocessor is configured to stop the I-TAT when the UE entersRRC_CONNECTED state.
 16. The UE according to claim 9, wherein themessage includes a value for the time alignment timer (I-TAT).